"Me versus just us versus us all" categorization and cooperation in nested social dilemmas.

In its generic form, a social dilemma poses a conflict between private and collective interests. People are often faced, however, with a conflict between private, (sub)group, and collective interests. This study examines participants simultaneous weighing of these 3 nested interests. The results show that increasing the salience of social categorization of any level of the hierarchy (i.e., 6 individuals, 2 subgroups, 1 collective) increases participants' concern for and contributions to the corresponding levels of interest (Experiment 1). One can promote concern for and contributions to the collective interest, which are lowest under categorization as 2 subgroups, by individuating the members of the individuals' own subgroup and/or the opposing subgroup (Experiment 2) and by cross-categorization with the opposing subgroup (Experiment 3).